1. Field of the Invention
The present invention relates to a stereoscopic imaging arrangement and to a stereoscopic viewing arrangement for use with such an imaging arrangement.
2. Description of Related Art
Numerous stereoscopic imaging and/or viewing arrangements are known. For example GB 606,065 discloses an arrangement for viewing scale models in stereoscopic fashion wherein a viewing tube containing an objective lens and a further lens is combined with two mutually orthogonal mirrors which divert light exiting from left and right regions of the further lens to respective eyepieces of a binocular viewing arrangement. GB 606,065, which dates from 1948, also refers to an even earlier stereoscopic eyepiece, as described in GB 167,130, for microscopes. This stereoscopic eyepiece comprises two tubes for binocular viewing, a single objective, and reflecting prisms positioned so that rays of light passing through the right-hand aide of the objective are reflected to the left and then into one viewing tube and rays of light passing through the left-hand side of the objective are reflected to the right and then into the other viewing tube.
Also U.S. Pat. No. 2,639,653, which dates from 1949, discloses a camera arrangement for taking microphotographs comprising a microscope having a blocking diaphragm which is used to obscure the left half and then the right half of the objective lens of a microscope. The respective photographs taken in this manner can be viewed through a stereoscope to give a three-dimensional impression of the object. It is stated at Col. 3 lines 15 to 18 that the blocking diaphragm may be located before or after the objective lens and within its focal point.
More recently stereoscopic endoscopes have been developed. In view or the size constraints on an endoscope, it is highly desirable to minimise the transverse dimensions of the optical system and for this reason many designs utilize a single objective and a beam splitting arrangement in its optical path which separates the light forming the left and right images.
For example U.S. Pat. No. 5,222,477 discloses a stereoscopic endoscope arrangement wherein an aperture plate is located adjacent the objective lens of a video camera assembly in the distal tip of the endoscope. Left and right apertures of the plate are opened alternately by a shutter which is coupled to a video switching arrangement. In this manner left and right images are detected in rapid succession and are alternately displayed on a monitor screen so that they can be viewed stereoscopically by means of a pair of spectacles in which the left and right eyepieces are occluded alternately in rapid succession in synchronism with the display. Such display systems are commercially available.
However the above shutter arrangement has the disadvantage that it cannot easily be retrofitted to an existing monocular endoscope. Furthermore the addition of shutter components to the tip portion of the endoscope tends to increase its bulk, which is undesirable.
GB-A-2,268,283 (which was published after the priority date of the present application) discloses an arrangement comprising a monocular endoscope having two mutually orthogonal reflecting surfaces disposed symmetrically at the exit pupil with their intersection vertical and intersecting the optical axis such that rays originating from the left hand region of the objective are separated from rays originating from the right hand region. The two sets of rays are focused onto respective television tubes and the resulting images are displayed by means of two orthogonal monitor screens which display cross-polarised images and have a partially reflecting surface disposed symmetrically between them. In this manner the images are combined and can be viewed stereoscopically by a user wearing polarising spectacles with cross-polarized lenses.
The provision of a beam splitting arrangement at the exit pupil of the endoscope in accordance with GB-A-2,268,283 avoids some of the above-noted problems of the arrangement of U.S. Pat. No. 5,222,477 but requires precise arrangement of the optical axis of the beam splitter with the optical axis of the endoscope and also requires that the rays exiting from the ocular of the endoscope are parallel. Furthermore the provision of a beam-splitting arrangement undesirably increases the number of reflecting surfaces and adds to the expense of the apparatus.